The project is designed as a clinical trial of the National Institute of Child Health and Human Development (NICHD) pertussis toxoid on children ages 18 months to 23 months. The contractor, the University of Goteborg, has a unique population of children since they are not routinely immunized to pertussis under the age of five. The objective of this study is to determine the effectiveness of the NICHD developed vaccine on this unimmunized population.